Caption: Eye lens. Coloured scanning electron micrograph (SEM) of cells from the lens (crystalline lens) of the eye. The cells are in a stacked linear, fibre-like arrangement. The transparency of the lens is thought to arise from this regular interlocking arrangement, as well as the absence of nuclei and the cells mainly containing the protein crystallin. The lens (found at the front of the eye) focuses light on to the light-sensitive cells in the retina at the back of the eye.